This invention relates to a defoamer composition comprising (a) hydrophobic silica; (b) a linear polysiloxane having end-blocked polyoxypropylene groups; (c) a polysiloxane having a pendant polyoxypropylene group; (d) a nonionic surfactant; and preferably (e) an inert diluent. The defoamer compositions are used in paints and coatings.
A defoamer is often an essential component to a paint or coating. Without a defoamer, bubbles will form in the paint or coating. When the paint or coating is applied to the substrate, the bubbles will dry on the substrate. These dried bubbles are not aesthetically pleasing. Furthermore, a substrate with dried bubbles is not effectively covered and protected from the environment.
Polysiloxanes are often used in defoamer compositions. When used in such compositions, the polysiloxane is usually added to the xe2x80x9cgrindxe2x80x9d component that diminishes defoamer xe2x80x9cpersistencyxe2x80x9d. Polysiloxane defoamers must be used judiciously in coatings to minimize xe2x80x9cfish eyexe2x80x9d formation that result from high surface tension differences between the product and substrate. Despite their outstanding foam destroying properties, polysiloxane at levels of 500 ppm can cause severe film defects, since even slight incompatibility between the surface and the coating can result in gloss reduction.
Linear polysiloxane having repeating internal siloxane moieties and an end blocked polypropylene oxide moiety are known. U.S. Pat. No. 3,562,786, which are hereby incorporated by reference, discloses defoaming compositions containing a polysiloxane having a pendant polyoxyalkylene group and an organic surfactant. The polyoxyalkylene group of the polysiloxane contains both polyoxyethylene and polyoxypropylene moieties. Polysiloxanes containing pendant polyoxypropylene moieties bonded to a dimethylsiloxane moiety are also known. See U.S. Pat. Nos. 5,558,806 and 5,534,609.
This invention relates to a defoamer composition comprising:
(a) hydrophobic silica;
(b) a linear polysiloxane having end-blocked polyoxypropylene groups;
(c) a polysiloxane having a pendant polyoxypropylene group; and
(d) a nonionic surfactant.
The defoamer preferably also contains a diluent.
The defoamer compositions are used in paints and coatings. The pendant group of component (c) is a polyoxypropylene group, and does not contain a polyoxyethylene group. An advantage of the defoamer is that it can be added to the paint formulation after it is formulated and will not degrade even after an extended shelf life. It is particularly compatible and widely effective in high gloss systems that are difficult to defoam. The defoamer compositions can be stored at temperatures of 0xc2x0 C. to 40xc2x0 C. for several months (typically up to six or even twelve months), without a phase separation, before using them.
Component (a) is hydrophobic silica. The hydrophobic silica preferably has a surface energy of from about 10 to about 40 dynes/cm2, preferably from about 20 to about 30 dynes/cm2. Preferably, the hydrophobic material is precipitated hydrophobic silica or a hydrophobic wax having an average particle size of from 5 to 75 microns, preferably 10 to 15 microns. Precipitated hydrophobic silica is made by treating hydrophilic silica with silicone according to well-known methods. Such precipitated hydrophobic silica can be purchased from Degussa, Georgia Kaolin, and J. M. Huber.
Component (b) is a linear polysiloxane having end-blocked polyoxypropylene groups, preferably having the following structural formula: 
where x is from about 12 to about 25 and n, which may be the same or different for each polyoxypropylene group, is from about 8 to 15, preferably about 12.
Component (c) is a polysiloxane containing pendant polyoxypropylene groups, preferably having the following structural formula: 
where x is from about 50 to about 80, y is from about 7 to about 9, and n is from about 8 to 15, most preferably where x=about 65, y=about 8, and n=about 12. The weight ratio of (I) to (II) is typically from 30:100 to 70:100, preferably from 50:100.
Component (d) is a nonionic surfactant having an average molecular weight of from about 300 to about 5,000, preferably from about 900 to about 1100, and a weight ratio of hydrophobic segment to hydrophilic segment of about 5 to about 2 preferably from about 3 to about 2. Preferably, polyethylene glycol monooleate is used as the nonionic surfactant.
The defoamer composition preferably contains a diluent. A wide variety of diluents can be used, e.g. water immiscible fluids such as liquid hydrocarbons having a pour point in the range of about xe2x88x9240xc2x0 C. to xe2x88x9210xc2x0 C. Preferably used, as the diluent, is polypropylene glycol having an average molecular weight of preferably from about 1500 to about 2500.
The amounts of the components used to make the defoamer are as follows, where the weight percents are based upon the total weight of defoamer:
(a) from 40 to 75 weight percent of diluent, preferably 45 to 70, weight percent;
(b) from 1 to 10 weight percent of hydrophobic silica, preferably 5 to 10;
(c) from 5 to 25 weight percent of a linear polysiloxane, preferably 5 to 15 weight percent;
(d) from 5 to 30 weight percent of a polysiloxane having pendant polyoxypropylene group, preferably 10 to 25 weight percent; and
(e) from 3 to 15 weight percent of a nonionic surfactant, preferably 5 to 12, most preferably from 6 to 10 weight percent.
Optional components of the defoamer include sorbitan tristearate, waxes, other surfactants, fatty acid esters, and end capped propylene oxide and/or butylene oxide polymers.
The defoamers can be stored at temperatures of 0xc2x0 C. to 40xc2x0 C. for several months (typically up to six or even twelve months) before using them without a phase separation. They are typically mixed in paints or coatings, preferably latex emulsions, in amounts of 0.01 to 2.0 part by weight based upon the weight of the latex emulsion, preferably from 0.2 to 0.8 part by weight.
Such formulated paints and coatings may include one or more of the following components in a addition to a defoamer: (1) 5.0 to 75.0 parts by weight of a latex emulsion (2) 20.0 to 60.0 parts by weight of water; (3) 1.0 to 40 parts by weight of a pigment; (4) 1.0 to 10.0 parts by weight of a polymeric binder; (5) 1.0 to 10 parts by weight of a coalescing aid; (6) 1.0 to 10.0 parts by weight of a thickener; (7) 0.1 to 2.0 parts by weight of a dispersant; (8) 0.01 to 1.0 part by weight of a biocide; (9) 1.0 to 25.0 parts by weight of a pigment; (10) 5.0 to 40.0 parts by weight of an extender pigment; (11) 1.0 to 5.0 parts by weight of a rheology modifier; (12) 1.0 to 5.0 parts by weight of a glycol, e.g. propylene glycol; (13) 0.1 to 2.0 parts by weight of a surfactant; and/or (13) 0.01 to 2.0 parts by weight of a base, e.g. ammonium hydroxide.